//提取常用的css样式
@mixin flex($hov:space-between,$col:center){
    display:flex;
    justify-content:$hov;
    align-items:$col;
  }

  @mixin bgImg($w,$h,$url,$size:contain){
    display: inline-block;
    width: $w;
    height: $h;
    background: url($url) no-repeat center;
    background-size: $size;
  }

